A particle grinder is a well known apparatus which includes generally a cylindrical container which has a horizontal axis, or an axis slightly inclined to the horizontal; a shaft with an outwardly diverging truncated cone is generally disposed along the axis. The materials to be ground are introduced to the interior of the container, which is provided with a resistant interior lining, so that the material to be ground, most frequently balls or the like, can be received in the apparatus. Subsequently the apparatus is made to rotate about its axis at a speed conveniently selected so that the material to be ground is carried along with the rotation and then falls back to the substances to be ground.
Machines of this type, which are to all intents and purposes, indispensable, have, however, a disadvantage, as they are very noisy, and in certain plants, for example in cement-producing plants, they constitute the major source of noise. The relatively large dimensions of these machines in many cases makes it very expensive to noise-proof the buildings in which they are situated.
It is clearly possible to surround the container exteriorly by a certain number of layers of sound-isolating material, but it will be borne in mind that threaded bolts for keeping sheeting in place pass through the container. Moreover the sound-isolating materials are fragile and of low mechanical rigidity. They must be protected on one hand against atmospheric decontamination, and on the other hand against dust which can pass into the container by the openings through which the threaded rods or bolts pass. Experience has shown that the dust, because of the vibrating action of the machine, can accumulate in the sound-isolating material, and can rapidly make it inoperative.
Furthermore the tightening nuts of the threaded bolts must remain accessible, so as to limit the time of replacing the sheeting elements. If the nuts exert a pressure on the sound-isolating material, the sound-isolating material is crushed and poorly protected against any dust. If one desires to dispense with this sound-isolating material in the vicinity of each rod by, for example, tightening a nut near the end of a corresponding shaft, the nut must be given sufficiently large dimensions so that it can easily be handled by tightening tools, and furthermore so that a leak-proof washer can be placed around the rod, in which case any noise reduction previously obtained is severely impaired.
An improvement in lined drums of ball mills is, for example, taught by Newell, in British Pat. No. 512,600; this reference is, however, silent as to sound-proofing the device. Neither does Venot-Pic, in French Pat. No. 72.32523, which relates to linings in an oven, provide any suggestion as to how to sound-proof the drum or container of a particle grinder, ball mill, rod mill or the like. Linco, in German laid-open patent specification DT No. 23 37 163 Al relates to a fastening device designed to alleviate stresses in ovens or the like, but is not concerned with sound-proofing the oven.
The objects of the invention, relating to an improvement in a particle grinder, and lined container thereof, or in a ball mill with a lined drum will be outlined in what follows.